This invention pertains to an ignition system for an internal combustion engine with a device to prevent the engine from revolving at more than a given r.p.m. and more particularly to a device to normally operate the ignition system upon the engine revolving at less than the given r.p.m. and to override the ignition system upon the engine revolving at more than the given r.p.m. so that the engine non-operates.
In general, there have been two types of a device for preventing an internal combustion engine from revolving at more than the predetermined speed. One of the devices comprises a switching element connected in series to a primary circuit of an ignition system, wherein when the engine revolves at more than the predetermined r.p.m., the switching element is opened so that the primary current through the primary circuit is continuously interrupted. The other device comprises a switching element connected in parallel to a breaker in a primary circuit of an ignition system, wherein when the engine revolves at more than the predetermined r.p.m., the switching element is closed to thereby override the breaker. In these prior devices, there is required a detector to electrically detect the revolution number of the engine for the operation of the switching elements, which detector conventionally employs the conduction and interruption of the primary current through the ignition system.
However, one of the most disadvantages of the prior arts is that the detector cannot detect or can unstably detect the revolution number of the engine when the device is operative because the primary current remains interrupted while the switching element of the first type of the device is opened or because the constant current continues to flow through the primary circuit while the switching element of the second type of the device is closed. Therefore, during the operation of the device, the detector cannot detect the revolution number of the engine and therefore, when the r.p.m. of the engine becomes lower than the predetermined value, the ignition system cannot retrieve its normal operation.